Sounds like the training partner is an asshole. If he would have been polite and asked to work in and the dude rolled his eyes and said no, then maybe I could see some words being exchanged.
Of course, I consider proper gym etiquette to always ask to work in and expect to hear the person say "no problem." We're all in there for the same reason - to stay physically fit.
I asked a guy the other week how many sets he had left (cable crossover). He said 4 or something and followed immediately with "you can work in." I declined. I went and did some box squats then went and hit the cable crossover. I was bigger than him (by probably 30lbs) but I didn't need to act like an asshole.